Move devstack launch jobs to launch slave.

Also add python-jenkins because I missed it earlier.

Change-Id: I516370da73e50b121849d7c22c5d92166ddf8238
Reviewed-on: https://review.openstack.org/24495
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins